CFW produces drying systems for fish feed production. Batch or continuous drying equipment that is highly energy-efficient can be supplied. Our engineers carefully consider the ambient conditions in the location and the customer’s specifications before implementing a solution, as “one size fits all” dryers often do not produce optimal results.

Modern dry fish feed often consists of pellets or flakes, which may be expanded, partially extruded or steam-pelleted. Pelleting fish feed ensures that it is more water-stable and less prone to breakage during transport and handling. The product needs to fulfil many requirements for aquaculture operations to be economical and sustainable, not least because feed costs can form up to 70% of the total production costs. The environmental impact of fish feed has also come under scrutiny in recent years.

The product is heat-treated and dried. The reduction in moisture content helps to prevent bacterial and fungal growth that reduces product safety and quality, which is one reason for preferring dry feeds. Another is the fact that handling and storage become easier. Both manual and automatic feeding is simplified and it becomes much easier to formulate the feeding programme according to nutritional requirements. In short, not only is the feed of a higher and more even quality, but the provision of the feed can be made more consistent and reliable.

Drying can have high energy costs and can thus affect fish feed prices considerably. Selecting the right drying equipment and technology is therefore of critical importance. To prevent product losses and maintain quality standards, the drying process must also be dependable and suited to the product. The digestibility of feed proteins, for instance, can vary according to the drying processes that are used. Product deformation may also occur.

Designing, operating and controlling dryers to maintain quality while controlling costs thus often calls for custom solutions.

The pellet texture and size influences feed uptake. A large proportion of fines resulting from breakage, or granules that are undersized, leads to uneaten feed particles floating in the water. This can reduce oxygen levels and water quality, affecting the health of the fish as well as increasing feed use unnecessarily.

The variables affecting the drying process and the desirable characteristics of the final product include:

• the moisture adsorption properties of the product,
• the air temperature,
• drying time,
• airflow velocity.

Drying often proceeds in several stages. Extruded products are hot on being formed, and some flash evaporation occurs that reduces the moisture content considerably as the fish feed starts to cool. Drying rates drop quickly as moisture must move through the pellet to reach the surface.

For maximum efficiency, airflow must not be too high. If the surface of the product is dried much more rapidly than diffusion can move moisture to the surface, energy costs will increase without shortening the drying time. It can also increase the risk of case hardening.

Where there are different drying zones in use, hot air or fluidised bed systems may be followed by belt or countercurrent dryers. The final moisture content is usually about 8 to 10%. Studies show that carefully controlled belt and countercurrent dryers with multiple decks can both maintain high drying rates. Countercurrent dryers tend to be more energy efficient, while belt dryers have the reputation of ensuring more consistently even drying.